270 



KNOWLEDGE. 



[December, 1901. 



a most strange peculiarity. As in lemurs generally, the 

 thumb is capable of being opposed to the index finger, 

 which is short ; the latter, together with the fourth and 

 fifth digits, being of normal thickness and provided 

 with long compressed and pointed claws. The third, 

 or middle finger, as is beautifully shown in the plate, 

 is, however, quite unlike the others, beingr extremely thin 

 and spider-like. Of its use. mention will be made later. 



This attenuated middle finger is one of two marked 

 peculiarities whereby the aye-aye differs so strongly from 

 its relatives, the true lemurs. Its other peculiarity is 

 to be found in its dentition. Ordinary lemurs, it may 

 be observed, have from 32 to 36 teeth ; the incisor, or 

 front teeth, although presenting certain peculiarities of 

 fonn, agreeing numerically with those of monkeys and 

 man in most cases. In the aye-aye, however, there are 

 only 18 teeth, all told; the incisors being reduced to a 

 single pair in each jaw, the canines, or tusks, wanting, 

 and the cheek-teeth, or grinders, comprising four pairs 

 in the upper and three in the lower jaw. Nor is this 

 all, for the incisors, which grow throughout life, are 

 large somewhat chisel-like teeth, recalling in many 

 respects those of the beaver, or other rodents, although 

 with peculiarities of their own which render them easily 

 distinguishable from those of all the members of that 

 group. Still, the whole character of the dentition is so 

 essentially rodent-like that there is little wonder the 

 old naturalists regarded the aye-aye as a near relative 

 of the squirrels. 



The general anatomy of the aye-aye, especially the 

 structure of its skull, shows, however, that it is 

 fortainly a near relative of the lemurs, themselves 

 distant cousins of the monkeys, from which, among 

 many other peculiarities, they differ by their expression- 

 less, fox-like faces. The aye-aye is therefore classed as 

 a lemui'oid ; of which group, owing to the peculiar 

 character of its dentition and its attenuated middle 

 finger, it must be regarded as a highly abeiTant and 

 specialised member. 



Unfortunately, iu spite of recent explorations in the 

 superficial deposits of Madagascar, where bones of huge 

 extinct lemuroids have been disinterred, nothing what^ 

 ever is known as to the ancestry of the aye-aye. 

 Evidently, however, it must be a comparatively ancient 

 type, for, if we may judge from the analogy of other 

 groups, a long period of time must have been required 

 to allow of the gradual evolution and development of 

 its characteristic peculiarities of dental and manual 

 structvire. 



Clearly these pecidiarities must be connected with 

 its mode of life. And we learn from those who have 

 obsei-ved tko creature iu its native forests or in cap- 

 tivity, that the aye-aye, unlike the true lemurs, subsists 

 largely upon wood-boring insect larva;, especially on the 

 lai-va of a beetle known to the Malagasy by the name 

 of andraitra. Apparently the aye-aye possesses a sense 

 of hearing so acute that when on a bough it can detect 

 the faint rasping sound made by the jaws of the 

 andi-aitra as it bores its way through the wood in the 

 interior. Thereupon it at once sets to work with its 

 powei-ful front teetli to chi.scl away the intervening 

 wood till it opens up the tunnel of the burrowing larva. 

 As soon as the tunnel is opened up the attenuated 

 middle finger is thnist in, cither to act as a probe to 

 determine the position of the larva, or to drag it out 

 from its hiding place, or perhaps for both piu-poses. 

 Some uncei-tainty still obtains as to the exact details of 

 these and other operations of a like nature, for our 

 infonnation on these points appears to be mainly, if 



not exclusively, based on native accoimts. There is, 

 however, little doubt that the vwdus operandi is in the 

 main as described above. 



Wo thus have a sufficient and satLsfactory explana^ 

 tion of the reason why the aye-aye differs so remarkably 

 in its dentition and in the structiu'e of its hand from 

 all its living kindred. If, however, we attempt to 

 account for the gradual development of these pecii- 

 liarities by what is commonly called natural selection, 

 W'e encounter considerable difhcvilty. It is easy to conceive 

 how the ancestors of the horse may have lost their lateral 

 toes by disuse, but how an ancestral aye-aye gradually 

 reduced the size of its middle finger till it assumed the 

 attenuated proportions of its existing rejiresentative is 

 veiy hard to understand, seeing that a slight diminution 

 in the calibre of this digit would be' of little or no 

 advantage. Some much more potent cause than 

 " natural selection " seems necessary in this, as in many 

 other instances. 



As regards its general mode of life, the aye-aye 

 wanders through the silent forests at night in pairs, 

 and never appears to associate with others of its fellows 

 than its partner. Probably the partnership is for life, 

 but on this point we have no definite information. The 

 aye-aye is one of the comparatively few mammals which 

 build a regular nest; this being constructed, according 

 to Mr. Baron, of the carefully rolled up leaves of one 

 particular kind of tree, and lined with small twigs and 

 dry leaves ; the whole structure having a diameter of 

 about a couple of feet. Apparently the sole use of this 

 nest is a nursery, and iu it at the proper season the 

 female brings forth a solitary offsjjring ; whether born 

 naked or clothed with hair does not seem to be ascer- 

 tained. The female alone builds the nest, which is 

 placed securely in the fork of a tree. In addition to 

 the use described above, the attenuated middle finger 

 is employed to comb the hair and clean the eyes, mouth, 

 and nose ; when thus engaged the animal generally 

 suspending itself head-downwards from a bough by its 

 hind-feet; — at any rate, this is the case in captivity. 

 Generally the food is not held in the paws after the 

 usual monkey and lemur fashion, although the act of 

 drinking is performed in an ape-like manner, the fingers 

 being first dipped in water and then sucked. 



In addition to the boring larvEe already alluded to, 

 it is certain that the aye-aye will eat various other 

 kinds of food, although native accounts differ tO' a con- 

 siderable extent on this point. Some say, for instance, 

 that it subsists largely on birds and their eggs, while 

 others assert that honey is its favourite food. Probably 

 there is some degree of truth in all these accounts, and 

 that the creature is to a certain extent omnivorous. 

 It will eat sugar-cane with considerable gusto, and in 

 captivity has been known to t-ake bananas. But that 

 these latter are not its natural food w'ould seem to be 

 evident from the fact that they stick in and clog its 

 teeth. 



As regards its distribution, the aye-aye is a very local 

 animal ; its chief habitat being the great forest clothing 

 the eastern border of the great central plateau of the 

 island. Here, however, it is apparently restricted to 

 the district forming the confines of the provinces of 

 Sihanaka and Betsimisaraka, which is situate about 

 five-and-twenty miles inland in latitude 17° 22' S. I 

 am, however, informed by the friend mentioned above 

 that an aye-aye occurs in the south of the island, which, 

 if its habitat is isolated from that of the typical form 

 may tiu-n out to be a new local race, or jiossibly even 

 a distinct species. 



